Photocell circuits provide a number of benefits that makes them desirable to use in a number of circumstances, particularly when a light source housing a photocell is in an environment exposed to sunlight or another light source. Photocells often function to measure the amount of ambient light in the area immediately surrounding the photocell in order to determine whether there is a need for a light source to be on or off. In a typical light source that employs a photocell, the photocell will detect a level of ambient light, and will activate the light source upon the darkening of ambient light below a predetermined level. When a certain amount of ambient light exceeds and/or meets the predetermined level, the photocell will deactivate the light source; conversely, when the certain amount is less than and/or meets the predetermined level, the photocell will activate the light source.
Photocells often have resistances that vary greatly depending on the level of ambient light. For example, a photocell can have a resistance of 70 KΩ during a moonlit night, while having a resistance of just 300Ω during an overcast day. The variance in resistance is an important feature of a photocell, because it controls whether or not the light source is on or off as a result of changes in ambient light, and the consequent changes in resistance.
Photocells are commonly used because they are small and inexpensive, and because they do not use a great deal of power. Photocells can, however, short-circuit or become open circuits. A photocell circuit that has become an open circuit will have many of the characteristics of a normally operating photocell in a dark environment; accordingly, detecting faults in the photocell circuit can be difficult.
Regular testing of photocells is important due to the placement of light sources containing photocells in exterior environments, such as streets, airports, and remote locations. However, in order to accurately test the functionality of a photocell, the photocell must be surrounded by a dark environment. This requires the testing to be performed in the middle of the night, or in a simulated night environment. Moreover, in certain industrial or commercial settings the photocell is disposed at a location that is difficult to reach by a user and/or a height above a ground surface that poses significant injury risks to a user.
Existing methods of testing photocells require the user to create a dark environment surrounding the photocell. Such methods include blacking out the area surrounding the photocell, such as the light source, with dark tape, thereby simulating a dark environment; however, this method is time-consuming, cumbersome, and often leaves sticky residue on the light source housing the photocell. Moreover, because of the location of many photocells, utilizing this method increases the risk of injury to the user.